Monocentric autostereoscopic optical apparatus and method

ABSTRACT

A monocentric autostereoscopic optical apparatus ( 10 ) for viewing a virtual image, electronically generated and projected on a curved surface. For each left and right image component, a separate optical system comprises an image generation system ( 70   l   , 70   r ) and projection system ( 72 ), the projection system comprising a spherical diffusive surface ( 40 ) and a ball lens ( 30 ) to provide wide field of view. A monocentric arrangement of optical components images the ball lens pupil ( 48 ) at the viewing pupil ( 14 ) and essentially provides a single center of curvature (C) for projection components. Use of such a monocentric arrangement, diffusive surface ( 40 ), and ball lens ( 30 ) provides an exceptionally wide field of view with large viewing pupil ( 14 ).

FIELD OF THE INVENTION

[0001] This invention generally relates to autostereoscopic displaysystems for viewing electronically generated images and moreparticularly relates to an apparatus and method for a monocentricarrangement of optical components to provide a very wide field of viewand large exit pupils.

BACKGROUND OF THE INVENTION

[0002] The potential value of autostereoscopic display systems is widelyappreciated particularly in entertainment and simulation fields.Autostereoscopic display systems include “immersion” systems, intendedto provide a realistic viewing experience for an observer by visuallysurrounding the observer with a 3D image having a very wide field ofview. As differentiated from the larger group of stereoscopic displaysthat include it, the autostereoscopic display is characterized by theabsence of any requirement for a wearable item of any type, such asgoggles, headgear, or special glasses. That is, an autostereoscopicdisplay attempts to provide “natural” viewing conditions for anobserver.

[0003] In an article in SID 99 Digest, “Autostereoscopic Properties ofSpherical Panoramic Virtual Displays”, G. J. Kintz discloses oneapproach to providing autostereoscopic display with a wide field ofview. Using the Kintz approach, no glasses or headgear are required.However, the observer's head must be positioned within a rapidlyrotating spherical shell having arrays of LED emitters, imaged by amonocentric mirror, to form a collimated virtual image. While the Kintzdesign provides one solution for a truly autostereoscopic system havinga wide field of view, this design has considerable drawbacks. Among thedisadvantages of the Kintz design is the requirement that the observer'shead be in close proximity to a rapidly spinning surface. Such anapproach requires measures to minimize the likelihood of accident andinjury from contact with components on the spinning surface. Even withprotective shielding, proximity to a rapidly moving surface could, atthe least, cause the observer some apprehension. In addition, use ofsuch a system imposes considerable constraints on head movement.

[0004] Another class of autostereoscopic systems operates by imaging theexit pupils of a pair of projectors onto the eyes of an observer,outlined in an article by S. A. Benton, T. E. Slowe, A. B. Kropp, and S.L. Smith (“Micropolarizer-based multiple-viewer autostereoscopicdisplay”, in Stereoscopic Displays and Virtual Reality Systems VI, SPIE,January, 1999). Pupil imaging, as outlined by Benton in theabove-mentioned article, can be implemented using large lenses ormirrors. An observer whose eyes are coincident with the imaged pupilsviews a stereoscopic scene without crosstalk, without wearing eyewear ofany kind.

[0005] It can be readily appreciated that the value and realisticquality of the viewing experience provided by an autostereoscopicdisplay system using pupil imaging is enhanced by presenting the 3-Dimage with a wide field of view and large exit pupil. Such a system ismost effective for immersive viewing functions if it allows an observerto be comfortably seated, without constraining head movement to within atight tolerance and without requiring the observer to wear goggles orother device. For fully satisfactory 3-D viewing, such a system shouldprovide separate, high-resolution images to right and left eyes. It canalso be readily appreciated that such a system is most favorablydesigned for compactness, to create an illusion of depth and width offield, while occupying as little actual floor space and volume as ispossible. For the most realistic viewing experience, the observer shouldbe presented with a virtual image, disposed to appear a large distanceaway.

[0006] It is also known that conflict between depth cues associated with“vergence” and “accommodation” can adversely impact the viewingexperience. Vergence refers to the degree at which the observer's eyesmust be crossed in order to fuse the separate images of an object withinthe field of view. Vergence decreases, then vanishes as viewed objectsbecome more distant. Accommodation refers to the requirement that theeye lens of the observer change shape to maintain retinal focus for theobject of interest. It is known that there can be a temporarydegradation of the observer's depth perception when the observer isexposed for a period of time to mismatched depth cues for vergence andaccommodation. It is also known that this negative effect on depthperception can be mitigated when the accommodation cues correspond todistant image position.

[0007] An example of a conventional autostereoscopic display unit isdisclosed in U.S. Pat. No. 5,671,992 (Richards), at which a seatedobserver experiences apparent 3-D visual effects created using imagesgenerated from separate projectors, one for each eye, and directed tothe observer using an imaging system comprising a number of mirrors.

[0008] Conventional solutions for stereoscopic imaging have addressedsome of the challenges noted above, but there is room for improvement.For example, some early stereoscopic systems employed special headwear,goggles, or eyeglasses to provide the 3-D viewing experience. As justone example of such a system, U.S. Pat. No. 6,034,717 (Dentinger et al.)discloses a projection display system requiring an observer to wear aset of passive polarizing glasses in order to selectively direct theappropriate image to each eye for creating a 3-D effect.

[0009] Certainly, there are some situations for which headgear of somekind can be considered appropriate for stereoscopic viewing, such aswith simulation applications. For such an application, U.S. Pat. No.5,572,229 (Fisher) discloses a projection display headgear that providesstereoscopic viewing with a wide field of view. However, where possible,there are advantages to providing autostereoscopic viewing, in which anobserver is not required to wear any type of device, as was disclosed inthe device of U.S. Pat. No. 5,671,992. It would also be advantageous toallow some degree of freedom for head movement. In contrast, U.S. Pat.No. 5,908,300 (Walker et al.) discloses a hang-gliding simulation systemin which an observer's head is maintained in a fixed position. Whilesuch a solution may be tolerable in the limited simulation environmentdisclosed in the Walker et al. patent, and may simplify the overalloptical design of an apparatus, constraint of head movement would be adisadvantage in an immersion system. Notably, the system disclosed inthe Walker et al. patent employs a narrow viewing aperture, effectivelylimiting the field of view. Complex, conventional projection lenses,disposed in an off-axis orientation, are employed in the devicedisclosed in U.S. Pat. No. 5,908,300, with scaling used to obtain thedesired output pupil size.

[0010] A number of systems have been developed to provide stereoscopiceffects by presenting to the observer the combined image, through abeamsplitter, of two screens at two different distances from theobserver, thereby creating the illusion of stereoscopic imaging, as isdisclosed in U.S. Pat. No. 5,255,028 (Biles). However, this type ofsystem is limited to small viewing angles and is, therefore, notsuitable for providing an immersive viewing experience. In addition,images displayed using such a system are real images, presented at closeproximity to the observer, and thus likely to introduce thevergence/accommodation problems noted above.

[0011] It is generally recognized that, in order to minimizevergence/accommodation effects, a 3-D viewing system should display itspair of stereoscopic images, whether real or virtual, at a relativelylarge distance from the observer. For real images, this means that alarge display screen must be employed, preferably placed a good distancefrom the observer. For virtual images, however, a relatively smallcurved mirror can be used as is disclosed in U.S. Pat. No. 5,908,300(Walker). The curved mirror acts as a collimator, providing a virtualimage at a large distance from the observer. Another system forstereoscopic imaging is disclosed in “Membrane Mirror BasedAutostereoscopic Display for Tele-Operation and TelepresenceApplications”, in Stereoscopic Displays and Virtual Reality Systems VII,Proceedings of SPIE, Volume 3957 (McKay, Mair, Mason, Revie) which usesa stretchable membrane mirror. The apparatus disclosed in the McKayarticle has limited field of view, due to the use of conventionalprojection optics and due to dimensional constraints that limit membranemirror curvature.

[0012] Curved mirrors have also been used to provide real images instereoscopic systems, where the curved mirrors are not used ascollimators. Such systems are disclosed in U.S. Pat. Nos. 4,623,223(Kempf); and 4,799,763 (Davis et al.) for example. However, systems suchas these are generally suitable where only a small field of view isneeded.

[0013] Notably, existing solutions for stereoscopic projection, projectimages onto a flat screen, even where that image is then reflected froma curved surface. This can result in undesirable distortion and otherimage aberration, constraining field of view and limiting image qualityoverall.

[0014] From an optical perspective, it can be seen that there would beadvantages to autostereoscopic design using pupil imaging. A systemdesigned for pupil imaging must provide separate images to the left andright pupils correspondingly and provide the most natural viewingconditions, eliminating any need for goggles or special headgear. Inaddition, it would be advantageous for such a system to provide thelargest possible pupils to the observer, so as to allow some freedom ofmovement, and to provide an ultra-wide field of view. It is recognizedin the optical arts that each of these requirements, by itself, can bedifficult to achieve. An ideal autostereoscopic imaging system must meetthe challenge for both requirements to provide a more filly satisfactoryand realistic viewing experience. In addition, such a system mustprovide sufficient resolution for realistic imaging, with highbrightness and contrast. Moreover, the physical constraints presented bythe need for a system to have small footprint, and dimensionalconstraints for interocular separation must be considered, so thatseparate images directed to each eye can be advantageously spaced andcorrectly separated for viewing. It is instructive to note thatinterocular distance constraints limit the ability to achieve largerpupil diameter at a given ultrawide field by simply scaling theprojection lens.

[0015] Monocentric imaging systems have been shown to providesignificant advantages for high-resolution imaging of flat objects, suchas is disclosed in U.S. Pat. No. 3,748,015 (Offner), which teaches anarrangement of spherical mirrors arranged with coincident centers ofcurvature in an imaging system designed for unit magnification. Themonocentric arrangement disclosed in the Offner patent minimizes anumber of types of image aberration and is conceptually straightforward,allowing a simplified optical design for high-resolution catoptricimaging systems. A monocentric arrangement of mirrors and lenses is alsoknown to provide advantages for telescopic systems having wide field ofview, as is disclosed in U.S. Pat. No. 4,331,390 (Shafer). However,while the advantages of monocentric design for overall simplicity andfor minimizing distortion and optical aberrations can be appreciated,such a design concept can be difficult to implement in an immersionsystem requiring wide field of view and large exit pupil with areasonably small overall footprint. Moreover, a fully monocentric designwould not meet the requirement for full stereoscopic imaging, requiringseparate images for left and right pupils.

[0016] As is disclosed in U.S. Pat. No. 5,908,300, conventionalwide-field projection lenses can be employed as projection lenses in apupil-imaging autostereoscopic display. However, there are a number ofdisadvantages with conventional approaches. Wide-angle lens systems,capable of angular fields such as would be needed for effectiveimmersion viewing, would be very complex and costly. Typical wide anglelenses for large-format cameras, such as the Biogon™ lens manufacturedby Carl-Zeiss-Stiftung in Jena, Germany for example, are capable of75-degree angular fields. The Biogon lens consists of seven componentlenses and is more than 80 mm in diameter, while only providing a pupilsize of 10 mm. For larger pupil size, the lens needs to be scaled insize; however, the large diameter of such a lens body presents asignificant design difficulty for an autostereoscopic immersion system,relative to the interocular distance at the viewing position. Costlycutting of lenses so that right- and left-eye assemblies could bedisposed side-by-side, thereby achieving a pair of lens pupils spacedconsistently with human interocular separation, presents difficultmanufacturing problems. Interocular distance limitations constrain thespatial positioning of projection apparatus for each eye and precludescaling of pupil size by simple scaling of the lens. Moreover, aneffective immersion system most advantageously allows a very wide fieldof view, preferably well in excess of 90 degrees, and would providelarge exit pupil diameters, preferably larger than 20 mm.

[0017] As an alternative for large field of view applications, balllenses have been employed for specialized optical functions,particularly miniaturized ball lenses for use in fiber optics couplingand transmission applications, such as is disclosed in U.S. Pat. No.5,940,564 (Jewell) which discloses advantageous use of a miniature balllens within a coupling device. On a larger scale, ball lenses can beutilized within an astronomical tracking device, as is disclosed in U.S.Pat. No. 5,206,499 (Mantravadi et al.) In the Mantravadi et al. patent,the ball lens is employed because it allows a wide field of view,greater than 60 degrees, with minimal off-axis aberrations ordistortions. In particular, the absence of a unique optical axis is usedadvantageously, so that every principal ray that passes through the balllens can be considered to define its own optical axis. Because of itslow illumination falloff relative to angular changes of incident light,a single ball lens is favorably used to direct light from space to aplurality of sensors in this application. Notably, photosensors at theoutput of the ball lens are disposed along a curved focal plane.

[0018] The benefits of a spherical or ball lens for wide angle imagingare also utilized in an apparatus for determining space-craft attitude,as is disclosed in U.S. Pat. No. 5,319,968 (Billing-Ross et al.) Here,an array of mirrors direct light rays through a ball lens. The shape ofthis lens is advantageous since beams which pass through the lens are atnormal incidence to the image surface. The light rays are thus refractedtoward the center of the lens, resulting in an imaging system having awide field of view.

[0019] Another specialized use of ball lens characteristics is disclosedin U.S. Pat. No. 4,854,688 (Hayford et al.) In the optical arrangementof the Hayford et al. patent, directed to the transmission of a2-dimensional image along a non-linear path, such as attached toheadgear for a pilot, a ball lens directs a collimated input image,optically at infinity, for a pilot's view. Another use for wide-angleviewing capabilities of a ball lens is disclosed in U.S. Pat. No.4,124,978 (Thompson), which teaches use of a ball lens as part of anobjective lens in binocular optics for night viewing.

[0020] With each of the patents described above that disclose use of aball lens, there are suggestions of the overall capability of the balllens to provide, in conjunction with support optics, wide field of viewimaging. However, there are substantial problems that must be overcomein order to make effective use of such devices for immersive imagingapplications, particularly where an image is electronically processed tobe projected. Conventional electronic image presentation techniques,using devices such as spatial light modulators, provide an image on aflat surface. Ball lens performance with flat field imaging would beextremely poor.

[0021] There are also other basic optical limitations for immersionsystems that must be addressed with any type of optical projection thatprovides a wide field of view. An important limitation is imposed by theLagrange invariant. Any imaging system conforms to the Lagrangeinvariant, whereby the product of pupil size and semi-field angle isequal to the product of the image size and the numerical aperture and isan invariant for the optical system. This can be a limitation whenusing, as an image generator, a relatively small spatial light modulatoror similar pixel array which can operate over a relatively smallnumerical aperture since the Lagrange value associated with the deviceis small. A monocentric imaging system, however, providing a large fieldof view with a large pupil size (that is, a large numerical aperture),inherently has a large Lagrange value. Thus, when this monocentricimaging system is used with a spatial light modulator having a smallLagrange value, either the field or the aperture of the imaging system,or both, will be underfilled due to such a mismatch of Lagrange values.For a detailed description of the Lagrange invariant, reference is madeto Modern Optical Engineering, The Design of Optical Systems by WarrenJ. Smith, published by McGraw-Hill, Inc., pages 4245.

[0022] Thus it can be seen that, while there are some conventionalapproaches that meet some of the requirements for stereoscopic imaging,there is a need for an improved autostereoscopic imaging solution forviewing electronically generated images, where the solution provides astructurally simple apparatus, minimizes aberrations and imagedistortion, and meets demanding requirements for wide field of view,large pupil size, and human interocular distance limitations.

SUMMARY OF THE INVENTION

[0023] It is an object of the present invention to provide anautostereoscopic optical apparatus for viewing a stereoscopic virtualimage.

[0024] According to one aspect of the present invention a monocentricautostereoscopic optical apparatus comprises a left image to be viewedby an observer at a left viewing pupil and a right image to be viewed bythe observer at a right viewing pupil, the apparatus comprising:

[0025] (a) a left optical system for forming the left image to be viewedat the left viewing pupil, the system comprising:

[0026] (1) a left image generation system for providing scene content,comprising a left image generator and a left relay lens for forming aleft intermediate image;

[0027] (2) a left projection system comprising a left spherically curveddiffusive surface for accepting the left intermediate image, the leftspherically curved surface having its center of curvature substantiallyconcentric with a left ball lens, the left ball lens spaced apart fromthe left spherically curved diffusive surface such that a left curvedimage is formed, the left curved image being a real image, the center ofcurvature of the left curved image coincident with the center ofcurvature of the left ball lens, the left ball lens having a left balllens pupil;

[0028] (b) a right optical system for forming the right image to beviewed at the right viewing pupil, the system comprising:

[0029] (1) a right image generation system for providing scene content,comprising a right image generator and a right relay lens for forming aright intermediate image;

[0030] (2) a right projection system comprising a right sphericallycurved diffusive surface for accepting the right intermediate image, theright spherically curved surface having its center of curvaturesubstantially concentric with a right ball lens, the right ball lensspaced apart from the right spherically curved diffusive surface suchthat a right curved image is formed, the right curved image being a realimage, the center of curvature of the right curved image coincident withthe center of curvature of the right ball lens, the right ball lenshaving a right ball lens pupil;

[0031] (c) a curved mirror, the curved mirror having its center ofcurvature placed substantially optically midway between the left balllens and the right ball lens;

[0032] (d) a beamsplitter disposed to reflect the left and right curvedimages toward the curved mirror, the curved mirror disposed to form avirtual stereoscopic image of the left and right curved images, and thecurved mirror disposed to form, through the beamsplitter, a real imageof the left ball lens pupil at the left viewing pupil and a real imageof the right ball lens pupil at the right viewing pupil.

[0033] A feature of the present invention is the use of a monocentricarrangement of optical components, which simplifies design, minimizesaberrations, and provides a wide field of view with large exit pupils.

[0034] A further feature of the present invention is the use of anintermediate diffusive surface within the optical system in order tomatch the low Lagrange invariant of a small image generator to the largeLagrange invariant of a projection system.

[0035] An alternative feature of the present invention is the projectionof light from an emissive curved surface. This arrangement helps tominimize the complexity of an autostereoscopic optical apparatus and thenumber of support optical components necessary.

[0036] It is an advantage of the present invention that it provides acompact arrangement of optical components, capable of being packaged ina display system having a small footprint.

[0037] It is a further advantage of the present invention that it allowshigh-resolution stereoscopic electronic imaging with high brightness andhigh contrast, with a very wide field of view. The present inventionprovides a system that is light-efficient and requires relatively lowlevels of light for projection.

[0038] It is an advantage of the present invention that it provides asolution for wide field stereoscopic projection that is inexpensive whencompared with the cost of conventional projection lens systems.

[0039] It is a further advantage of the present invention that itprovides stereoscopic viewing without requiring an observer to weargoggles or other device.

[0040] It is yet a further advantage of the present invention that itprovides an exit pupil of sufficient size for non-critical alignment ofan observer in relation to the display.

[0041] These and other objects, features, and advantages of the presentinvention will become apparent to those skilled in the art upon areading of the following detailed description when taken in conjunctionwith the drawings wherein there is shown and described an illustrativeembodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] While the specification concludes with claims particularlypointing out and distinctly claiming the subject matter of the presentinvention, it is believed that the invention will be better understoodfrom the following description when taken in conjunction with theaccompanying drawings, wherein:

[0043]FIG. 1 is a perspective view showing the use of apparatus of thepresent invention in an autostereoscopic imaging system;

[0044]FIG. 2 is a schematic view identifying key components of anautostereoscopic imaging system of the present invention;

[0045]FIG. 3 shows a cutaway view illustrating the concentricarrangement of a ball lens and diffusing surface at the intermediateimage plane, according to the present invention;

[0046]FIG. 4 is a cutaway view showing a conventional implementation forwide angle projection lenses for right-eye and left-eye imageprojection;

[0047]FIG. 5 is a schematic layout showing left-eye and right-eyeprojection systems in a preferred embodiment;

[0048]FIG. 6 shows a schematic layout in vertical cross-section of oneof the two projection systems with the curved mirror and beamsplitter,relative to observer position;

[0049]FIG. 7 shows an alternate embodiment for a projection opticsassembly, using a double-concave fiber faceplate as diffusive surface;

[0050]FIG. 8a shows an alternate embodiment in which projection systemsdirect light onto a curved mirror, without an interposed beamsplitter;

[0051]FIG. 8b shows an alternative embodiment in which the curved mirroris aspherical;

[0052]FIG. 9 shows a segmented, curved mirror in which segments sharesubstantially the same center of curvature;

[0053]FIG. 10 shows an alternate embodiment using a cylindricallycurved, reflective Fresnel lens in place of a curved mirror;

[0054]FIG. 11 shows another alternate embodiment in cross section, usinga flat emissive image-forming surface with a fiber faceplate;

[0055]FIG. 12 shows an alternate embodiment in cross section, using aspherically curved emissive image-forming surface; and,

[0056]FIG. 13 shows an alternate embodiment using a cathode-ray tube(CRT) having a curved image-forming surface.

DETAILED DESCRIPTION OF THE INVENTION

[0057] The present description is directed in particular to elementsforming part of, or cooperating more directly with, apparatus inaccordance with the invention. It is to be understood that elements notspecifically shown or described may take various forms well known tothose skilled in the art.

[0058] Referring to FIG. 1, there is shown a perspective view of anautostereoscopic imaging system 10. An observer 12 is typically seatedin position to view a virtual stereoscopic image from left and rightviewing pupils 14 l and 14 r. Optimal viewing conditions are obtainedwhen left and right eye pupils 68 l (not labeled in FIG. 1) and 68 r ofobserver 12 are coincident with the position of left and right viewingpupils 14 l and 14 r.

[0059] A right optical system 20 r directs an image through a right balllens 30 r to a beamsplitter 16. A right curved image 80 r is formed at afront focal surface 22 of a curved mirror 24, so as to be locatedbetween right ball lens 30 r and curved mirror 24.

[0060] It must be noted that, as shown in FIG. 1, there are twocomponents to the stereoscopic image seen by observer 12. Thestereoscopic image is a curved image 80, which comprises left curvedimage 80 l and a right curved image 80 r. Left curved image 80 l andright curved image 80 r differ sufficiently in scene content so as toproduce a stereoscopic 3-D effect. The stereoscopic image seen byobserver 12 comprises a left image that is viewed at left viewing pupil14 l and a right image that is viewed at right viewing pupil 14 r. As isrepresented in FIG. 1, the left and right optical paths cross in system10, due to imaging by curved mirror 24.

[0061] The description that follows primarily focuses on the opticalcomponents that direct light to either one of viewing pupils 14 l and 14r. It should be noted that, up to and including left and right ball lensassemblies 30 l and 30 r, similar optical components are employed forleft optical system 20 l and right optical system 20 r, that is, forboth left and right optical paths. For clarity, the description thatfollows applies to both right and left optical system 20 components. Anydistinction between right and left optical paths is made only whennecessary to be precise. (Appended left “l” or right “r” designators areomitted from this description unless needed.)

[0062] Referring again to FIG. 1, the stereoscopic image seen byobserver 12 is formed from curved image 80 by mirror 24 as a virtualimage. That is, the image does not appear to observer 12 as if projectedonto the surface of curved mirror 24; instead, the image appears to bebehind curved mirror 24, between the rear of curved mirror 24 andinfinity.

[0063]FIG. 1 illustrates the key problems to be solved, from an opticaldesign perspective, and shows an overview of the solution provided bythe present invention. It is instructive to review key designconsiderations for achieving the most life-like stereoscopic viewing. Inorder to provide an effective immersion experience, a wide field of viewis important, in excess of the 60 degrees available using prior arttechniques. In order to be used comfortably by observer 12, viewingpupils 14 l, 14 r must be sufficiently large. As design goals, thesystem 10 of the present invention is intended to provide a field ofview of at least 90 degrees with the diameter of viewing pupil 14 inexcess of 20 mm in diameter.

[0064] Referring to FIG. 2, there is shown a schematic view of keyoptical components in autostereoscopic imaging system 10. For simplicityin FIG. 2, only one of the left/right optical paths is represented. Inactual practice, autostereoscopic imaging system 10 comprises left andright optical systems 20 l and 20 r, where, for example, left opticalsystem 20 l comprises a left image generation system 70 l and a leftprojection system 72 l, with corresponding sub-components.

[0065] Keeping this dual arrangement in mind, optical system 20comprises image generation system 70. Image generation system 70, inturn, comprises an image generator 74, which provides the scene contentfor display. In a preferred embodiment, image generator 74 comprises aspatial light modulator 36 controlled by imaging circuitry (not shown)that provides an image as an array of pixels. In a manner well known inthe imaging arts, spatial light modulator 36 cooperates with a lightsource 34 and a polarizing beamsplitter 38 to form an image that isinput to a relay lens 54.

[0066] Relay lens 54, which can consist of a number of component lensesas is shown in FIG. 2, directs light received from image generator 74onto a diffusing element 32. A left or right intermediate image 76 l/76r is formed on a curved diffusive surface 40 of diffusing element 32. Aprojection system 72 comprises curved diffusive surface 40 and a balllens assembly 30. A stereoscopic projection system 82 comprises both aleft projection system 72 l and a right projection system 72 r. For bothleft and right projection systems 72 l/72 r, ball lens assembly 30projects left or right intermediate image 76 l/76 r to front focalsurface 22 of curved mirror 24 through a beamsplitter 16. Curved mirror24 forms a stereoscopic virtual image that appears, to observer 12, tobe “behind” curved mirror 24.

[0067] It can be appreciated that the arrangement of components shown inFIGS. 1 and 2 present a novel approach to the challenge of achievingwide field of view with a projection lens. By way of illustration, FIG.4 shows how a conventional approach to stereoscopic projection lensdesign would be implemented. As FIG. 4 shows, conventional lens designtechniques require the manufacture of fairly complex left-eye andright-eye lens assemblies 18 l, 18 r. In order for lens assemblies 18 land 18 r to project properly to each eye, lens assemblies 18 l and 18 rmust have their respective optical axes 26 l, 26 r within an appropriateinterocular distance 28 (that is, the distance between right and lefteyes of observer 12, nominally in the 60-70 mm range). This requiressome truncation of lens assembly 18 l and 18 r components, as indicatedby dotted lines A and B in FIG. 4. It can be appreciated by thoseskilled in the optical arts that conventional solutions such as thatshown in FIG. 4 can be costly and difficult to design and manufacture.In the present invention, as is best shown in FIG. 2 and FIG. 5, lensassembly 18 l/18 r is replaced by projection system 72, which comprisesa small number of components by comparison.

[0068] In contrast to the conventional approach as partially illustratedin FIG. 4, FIG. 5 shows another schematic view of left and right opticalsystems 20 l, 20 r of the present invention. Left and right opticalsystems 20 l and 20 r provide cooperating projection systems with axesthat are not necessarily parallel but, rather, directed towards adistant converging point. As described for FIG. 2, relay lens assemblies54 l and 54 r form left and right intermediate images 76 l and 76 rrespectively on curved diffusive surfaces 40 l and 40 r. To provide aviewable stereoscopic image over a large range of human interocularseparations, ball lens assemblies 30 l, 30 r are advantageouslyseparated by an averaged, empirically determined interocular distance28. Typical interocular distances are 55 mm to 75 mm. A preferredembodiment is 60 mm to 70 mm with 65 mm being optimal.

[0069] Operation of Ball Lens Assembly 30

[0070] Ball lens assembly 30 l/30 r functions as the projection lens forits associated left or right optical system 20 l/20 r. Referring to FIG.3, there is shown the concentric arrangement provided for each ball lensassembly 30. A central spherical lens 46 is disposed between meniscuslenses 42 and 44, where meniscus lenses 42 and 44 have indices ofrefraction and other characteristics intended to minimize on-axisspherical and chromatic aberration, as is well known in the opticaldesign arts. Stops 48 limit the entrance pupil within ball lens assembly30. Stops 48 need not be physical, but may alternately be implementedusing optical effects such as total internal reflection. In terms of theoptics path, stops 48 serve to define an exit pupil for ball lensassembly 30.

[0071] In a preferred embodiment, meniscus lenses 42 and 44 are selectedto reduce image aberration and to optimize image quality for the imageprojected toward curved mirror 24. It must be noted that ball lensassembly 30 could comprise any number of arrangements of support lensessurrounding central spherical lens 46. Surfaces of these support lenses,however many are employed, would share a common center of curvature Cwith central spherical lens 46. Moreover, the refractive materials usedfor lens components of ball lens assembly 30 could be varied, within thescope of the present invention. For example, in addition to standardglass lenses, central spherical lens 46 could comprise a plastic, an oilor other liquid substance, or any other refractive material chosen forthe requirements of the application. Meniscus lenses 42 and 44, and anyother additional support lenses in ball lens assembly 30, could be madeof glass, plastic, enclosed liquids, or other suitable refractivematerials, all within the scope of the present invention. In itssimplest embodiment, ball lens assembly 30 could comprise a singlecentral spherical lens 46, without additional supporting refractivecomponents.

[0072] Arrangement, Materials, and Composition of Diffusing Element 32

[0073] Referring again to FIG. 3, curved diffusive surface 40 isconcentric with ball lens assembly 30, centered at C. This concentricarrangement minimizes field aberrations for projection of the left/rightintermediate image 76 l/76 r formed on curved diffusive surface 40.Curved diffusive surface 40 can be considered as a myriad set ofdispersive point sources 50, whose rays are received by ball lensassembly 30. By providing an intermediate image on curved diffusivesurface 40, Lagrange invariant constraints on exit pupil size and fieldangle are effectively overcome. In terms of components shown in FIG. 1,curved diffusive surface 40 acts as an interface to match the lowLagrange invariant that is characteristic of image generation system 70with the high Lagrange invariant of stereoscopic projection system 82.By overcoming Lagrange invariant constraints, the use of curveddiffusive surface 40 thus allows wide angle projection of the image byball lens assembly 30.

[0074] The function of curved diffusive surface 40 is to diffuse thelight relayed from relay lens assembly 54, but with as much brightnessas possible, for projection at a wide image angle by ball lens assembly30. To allow eventual viewing of the projected image by observer 12, itis important that each point source 50 effectively fill stop 48 of balllens assembly 30. If this is achieved, observer 12, with eyes positionedat viewing pupils 14 l/14 r, can view the entire projected image fromany point within viewing pupils 14 l/14 r.

[0075] In the preferred embodiment, diffusing element 32 is a lenscoated in order to provide curved diffusive surface 40. Suitablediffusive coatings and treatments for curved diffusive surface 40 areknown to those skilled in the optical arts. Alternately, curveddiffusive surface 40 could be ground, etched, or treated in some otherway in order to provide the needed diffusive characteristics. Thecurvature of curved diffusive surface 40 is concentric with thecurvature of ball lens assembly 30 in order to provide an image forprojection that has no field aberrations and has minimum on-axisaberration.

[0076] In an alternate embodiment, diffusive surface 40 could beimplemented using a fiber optic faceplate 56, as is shown in FIG. 7,such as those manufactured by Incom, Inc., Charlton, Mass. Typicallyused in flat panel display applications, fiber optic faceplates 56transfer an image from one surface to another. As part of optical system20, fiber optic faceplate 56 would have a double-concave shape. The leftor right intermediate image 76 l/76 r would be focused on an inputconcave surface 58 and be transferred to an output concave surface 60that comprises curved diffusive surface 40. Output concave surface 60can be treated using a number of techniques familiar to those skilled inthe optical arts for enhancing the performance of curved diffusivesurface 40. Surface treatments could be achieved, for example, usingvarious grinding, buffing, etching, or other techniques that result in adiffusive surface, or using a holographic grating, for example. Adiffusive coating could alternately be applied to output concave surface60.

[0077] Monocentric Design of Image Path

[0078] The present invention utilizes the inherent advantages providedby a monocentric arrangement of the image path about monocentric axis Mand it's optical equivalent M¹ as shown in FIG. 1. Referring to FIG. 6,there is shown a vertical cross section of the optics path inautostereoscopic imaging system 10. The image from spatial lightmodulator 36 is relayed onto curved diffusive surface 40 l/40 r as leftor right intermediate image 76 l/76 r, as described above. Left/rightintermediate image 76 l/76 r on curved diffusive surface 40 is projectedby ball lens assembly 30 and reflected by beamsplitter 16 to form thestereoscopic intermediate curved image 80 comprising left and rightcurved images 80 l and 80 r near front focal surface 22 of curved mirror24. Stereoscopic intermediate curved image 80, itself a real image, issubstantially collimated by curved mirror 24 to present a virtual imageto observer 12. By means of beamsplitter 16 and curved mirror 24, theexit pupil of ball lens assembly 30 is imaged at unity magnification toviewing pupil 14. It must be noted that the design of the presentinvention is optimized for unity magnification; however, some variationfrom unity magnification is possible, within the scope of the presentinvention.

[0079] A common center of curvature is provided at center C of ball lensassembly 30. This point serves as center of curvature for ball lensassembly 30 with its component meniscus lenses 42 and 44 and for curveddiffusive surface 40. Because it is imaged at viewing pupil 14, center Cprovides an approximate center of curvature for curved mirror 24, asdescribed subsequently.

[0080] Referring to FIG. 5, it can be seen that left and right ball lensassembly 30 l/30 r each have a center, respectively annotated as C₁ andC_(r), with these centers separated by interocular distance 28. Theactual center of curvature of mirror 24, annotated C_(m) is halfwaybetween C₁ and C_(r). Thus, the arrangement of the image path issubstantially monocentric about axis M, with necessary adjustment, thatis, averaging, of some coordinates to locate a center point. Dueprimarily to interocular separation, geometrically perfectmonocentricity cannot be achieved. However, interocular distance 28 isrelatively small considering the overall scale of the system andeffectively allows spacing of viewing pupils 14 l, 14 r to each side ofa true center point.

[0081] Curved Mirror 24 Arrangement

[0082] Due again to interocular distance 28, the precise shaping ofcurved mirror 24 can be adjusted to vary to some degree from a precisespherical shape. An aspheric shape could be used for curved mirror 24,to minimize off-axis pupil aberration, for example.

[0083] Curved mirror 24 can be a fairly expensive component to fabricateusing traditional forming, grinding, and polishing techniques. It may bemore practical to fabricate mirror 24 from two or more smaller mirrorsegments, joined together to assemble one large mirror 24. Referring toFIG. 9, there is shown curved mirror 24 constructed using two or moresegments 64, each segment 64 being spherical and each segment 64 trimmedto join another segment 64 along a seam 62. With this arrangement,centers of curvature of each segment 64 would overlap each other.

[0084] As yet another alternative embodiment, curved mirror 24 maycomprise a membrane mirror, such as a Stretchable Membrane Mirror (SMM),whose curvature is determined by a controlled vacuum generated in anairtight cavity behind a stretched, reflective surface. Use of astretchable membrane mirror is disclosed in the McKay article,referenced above.

[0085] Curved mirror 24 can alternately be embodied using replicatedmirrors, Fresnel mirrors, or using one or more or retroreflectivesurfaces.

[0086] Referring to FIG. 8, there is shown an alternate substantiallymonocentric arrangement in which left and right optical systems 20 l and20 r project directly into curved mirror 24, without the use ofbeamsplitter 16 as was shown in FIGS. 1, 2, 6, and 9.

[0087] The arrangement of FIG. 8a requires that curved mirror 24 haveacceptable off-axis performance, since the image path for each viewingpupil 14 l and 14 r must be slightly off-center. Large or asphericmirrors could be employed, in conjunction with optical system 20comprising ball lens assembly 30 for wide-angle imaging. In order forthe arrangement shown in FIG. 8a to perform satisfactorily when using aspherical curved mirror 24, the ratio of off-axis distance to mirror 24focal length must be small. As a rule-of-thumb, it has been determinedthat curved mirror 24 having a spherical surface would performsatisfactorily provided that the off-axis angle does not exceedapproximately 6 degrees.

[0088] For off-axis angles in excess of 6 degrees, use of a curvedmirror 24 having an aspherical surface would be more suitable, as isshown in FIG. 8b. Center of curvature point C_(m)′ is chosen to bemidway between viewing pupils 14 l and 14 r. Center of curvature pointC_(m) in FIG. 5 is midway between center points C₁ and C_(r) of balllens assemblies 30 l/30 r. Such an aspherical design could be toroidaland would be monocentric with respect to axis E which passes throughpoints C_(m) and C_(m)′. In cross-section, curved mirror 24 fabricatedin this manner would be elliptical, with points C_(m) and C_(m)′ servingas foci of the ellipse.

[0089] Referring to FIG. 10, there is shown yet another alternatearrangement similar to that shown in FIG. 8b. In FIG. 10, curved mirror24 is implemented using a cylindrically curved, reflective Fresnelmirror 66. The arrangement of components shown in FIG. 10 is monocentricwith respect to monocentric axis M, as was shown in FIG. 8b. ReflectiveFresnel mirror 66 has power in only one direction. Reflective Fresnelmirror 66 can be, for example, a planar element fabricated on a flexiblesubstrate, similar to Fresnel optical components manufactured by FresnelOptics, Rochester, N.Y. Fresnel mirror 66 would be curved into agenerally cylindrical shape about axis E, as is shown in FIG. 10.Fresnel mirror 66 would image the exit pupils of ball lens assemblies 30l/30 r onto viewing pupils 14 l/14 r in a similar manner to thatdescribed above for curved mirror 24. Optical systems 20 l/20 r would beoptimized to accommodate Fresnel mirror 66 performance characteristics.

[0090] As yet another option, curved mirror 24 could be replaced using aretroreflective surface, such a surface having an essentially sphericalshape with center of curvature coincident with that of ball lensassembly 30. A retroreflective surface would not introduce theimage-crossing effect caused by curved mirror reflection. It must benoted, however, that this alternate arrangement would provide a realimage, not the virtual image formed by autostereoscopic imaging system10 in the preferred embodiment.

[0091] Image Source Alternatives

[0092] Spatial light modulator 36 of the preferred embodiment can be oneof a number of types of devices. Exemplary spatial light modulators 36include, but are not limited to, the following types:

[0093] (a) Liquid Crystal Device (LCD). Widely used in projectionapparatus for electronically generated images, LCDs selectively modulatethe intensity of an incoming optical beam from a light source 34(FIG. 1) in a space-wise fashion, through individual array elements thatproduce the individual pixels displayed. LCDs can be either transmissiveor reflective. The preferred embodiment uses reflective LCDs.

[0094] (b) Digital Micromirror Device (DMD) from Texas Instruments,Dallas, Texas. This type of reflective device could alternately beemployed to modulate an optical beam from a light source 34.

[0095] (c) Scanning devices that create a 2-D image using successivescans from a point source or from a linear array. Such scanning devicescould comprise a scanning laser or CRT, which generate images from pointsources. Such a point source could be used, for example, to write leftor right intermediate image 76 l/76 r onto diffusive surface 40.Alternately, a scanning device could comprise a linear device such as agrating light-valve (GLV), such as those manufactured by Silicon LightMachines, Sunnyvale, CA.

[0096] The above listing is representative only; other types of spatiallight modulators 36 or other image sources could alternately be employedto provide the source image, within the scope of the present invention.

[0097] It is important to note that telecentric behavior of relay lensassembly 54 is important for distortion-free imaging.

[0098] For clarity, only a single spatial light modulator 36 isrepresented for each left and right optical system 20 l/20 r in FIGS. 1,2, 5, 6, and 7. In actual autostereoscopic imaging system 10, each colorcomponent (typically Red, Green, and Blue, RGB) could require onespatial light modulator 36. Corresponding light sources 34 would beprovided in the component light colors, as is well known in theelectronic imaging art. The different image planes would be combined inorder to provide left and right intermediate images 76 l/76 r in colorat left and right curved diffusive surfaces 40 l/40 r. In a preferredembodiment, one spatial light modulator 36 having an integral colorfilter array is used, as is familiar to those skilled in the art. Asanother alternate embodiment, a color sequential arrangement of R, G,and B components could be provided from one spatial light modulator 36.Fortunately, light levels required for autostereoscopic imaging system10 using pupil imaging, as disclosed herein, are relatively low,relaxing a well-known constraint typical with imaging filters,susceptible to photo-degradation over time.

[0099] In an alternate embodiment, the function of providing anintermediate image at curved diffusive surface 40 could be performedwithout using spatial light modulators 36 and associated support optics.However, the limitation for optimum stereoscopic representation is thatthe intermediate image formed at the position of curved diffusivesurface 40 must be curved, with the center of curvature for thisalternate curved diffusive surface 40 coincident with center C of balllens assembly 30, as is described above in reference to FIG. 6.

[0100] Referring to FIG. 12, an emissive image forming surface 88 couldbe employed as an alternative. For example, an Organic Light EmittingDiode (OLED), available from eMagin Corporation, Hopewell Junction,N.Y., could be used as emissive image forming surface 88. Similarly,Polymer Light Emitting Diode (PLED) technology could be employed. Forthis application, OLED or PLED array technology allow an image surfaceavailable on a flexible, flat panel that could be molded to have aspherical curvature coincident with center C of ball lens assembly 30,as is shown in the cross-sectional view of FIG. 12. Here, an OLED orPLED array comprising emissive image forming surface 88, curved mirror24, and ball lens assembly 30 would be monocentric with respect to thesame symmetry axis.

[0101] Referring to FIG. 13, a cathode-ray tube (CRT) 90 could beemployed to provide emissive image forming surface 88. This wouldrequire a change of curvature from standard off-the-shelf CRTmanufacture, to provide the proper shape for cathode-ray tube 90.

[0102] As yet another alternative, a flat image-forming emissive surface84 could be employed, in conjunction with a fiber optic faceplate 56, asis shown in FIG. 11. Fiber optic faceplate 56 would require a flatsurface 86 facing such an emissive surface, with output concave surface60 facing ball lens 30 and concentric with center C, as was also used inthe alternate embodiment of FIG. 7.

[0103] The preferred embodiment of the present invention provides anexceptionally wide field of view for stereoscoping imaging in excess ofthe 90-degree range, with viewing pupil 14 size near 20 mm. Moreover,ball lens assembly 30 provides excellent off-axis performance and allowsa wider field of view, possibly up to 180 degrees. This provides anenhanced viewing experience for observer 12, without requiring thatheadset, goggles, or other device be worn.

[0104] The invention has been described in detail with particularreference to certain preferred embodiments thereof, but it will beunderstood that variations and modifications can be effected within thescope of the invention as described above, and as noted in the appendedclaims, by a person of ordinary skill in the art without departing fromthe scope of the invention. For example, there are many possiblearrangements for projection optics and mirror surfaces that could beused with the monocentric arrangement of components disclosed for thisinvention.

[0105] Thus, what is provided is a monocentric optical apparatus forautostereoscopic display, providing a very wide field of view and largeviewing pupils.

[0106] The invention has been described in detail with particularreference to certain preferred embodiments thereof, but it will beunderstood that variations and modifications can be effected within thescope of the invention.

Parts List

[0107]10. Autostereoscopic imaging system

[0108]12. Observer

[0109]14. Viewing pupil

[0110]14 l. Left viewing pupil

[0111]14 r. Right viewing pupil

[0112]16. Beamsplitter

[0113]18. Lens assembly

[0114]18 l. Left-eye lens assembly

[0115]18 r. Right-eye lens assembly

[0116]20. Optical system

[0117]20 l. Left optical system

[0118]20 r. Right optical system

[0119]22. Front focal surface

[0120]24. Curved mirror

[0121]26. Optical axis, right optical axis, left optical axis

[0122]28. Interocular distance

[0123]30. Ball lens assembly

[0124]30 l. Left ball lens assembly

[0125]30 r. Right ball lens assembly

[0126]32. Diffusing element

[0127]32 l. Diffusing element

[0128]32 r. Diffusing element

[0129]34. Light source

[0130]36. Spatial light modulator

[0131]36 l. Spatial light modulator

[0132]36 r. Spatial light modulator

[0133]38. Polarizing beamsplitter

[0134]38 l. Polarizing beamsplitter

[0135]38 r. Polarizing beamsplitter

[0136]40. Curved diffusive surface

[0137]40 l. Left curved diffusive surface

[0138]40 r. Right curved diffusive surface

[0139]42. Meniscus lens

[0140]44. Meniscus lens

[0141]46. Spherical lens

[0142]48. Stop

[0143]50. Dispersive point source

[0144]54. Projection lens assembly

[0145]54 l. Projection lens assembly

[0146]54 r. Projection lens assembly

[0147]56. Fiber optic faceplate

[0148]58. Input concave surface

[0149]60. Output concave surface

[0150]62. Seam

[0151]64. Segment

[0152]66. Fresnel mirror

[0153]68. Human eye pupil

[0154]68 l. Human eye pupil

[0155]68 r. Human eye pupil

[0156]70. Image generation system

[0157]70 l. Right image generation system

[0158]70 r. Left image generation system

[0159]72. Projection system

[0160]74. Image generator

[0161]76. Intermediate image

[0162]76 l. Left intermediate image

[0163]76 r. Right intermediate image

[0164]80. Curved image

[0165]80 l. Left curved image

[0166]80 r. Right curved image

[0167]82. Stereoscopic projection system

[0168]84. Flat image-forming emissive surface

[0169]86. Flat surface

[0170]88. Emissive image-forming surface

[0171]90. Cathode-ray tube

[0172] C. Center of curvature

[0173] M. Monocentric axis

[0174] M¹. Optical equivalent of monocentric axis M

What is claimed is:
 1. A monocentric autostereoscopic optical apparatusfor viewing a stereoscopic virtual image comprising a left image to beviewed by an observer at a left viewing pupil and a right image to beviewed by the observer at a right viewing pupil, the apparatuscomprising: (a) a left optical system for forming said left image to beviewed at said left viewing pupil, the system comprising: (1) a leftimage generation system for providing scene content, comprising a leftimage generator and a left relay lens for forming a left intermediateimage; (2) a left projection system comprising a left spherically curveddiffusive surface for accepting said left intermediate image, said leftspherically curved surface having a center of curvature substantiallyconcentric with a left ball lens, said left ball lens spaced apart fromsaid left spherically curved diffusive surface such that a left curvedimage is formed, said left curved image being a real image, a center ofcurvature of said left curved image coincident with a center ofcurvature of said left ball lens, said left ball lens having a left balllens pupil; (b) a right optical system for forming said right image tobe viewed at said right viewing pupil, the system comprising: (1) aright image generation system for providing scene content, comprising aright image generator and a right relay lens for forming a rightintermediate image; (2) a right projection system comprising a rightspherically curved diffusive surface for accepting said rightintermediate image, said right spherically curved surface having acenter of curvature substantially concentric with a right ball lens,said right ball lens spaced apart from said right spherically curveddiffusive surface such that a right curved image is formed, said rightcurved image being a real image, a center of curvature of said rightcurved image coincident with a center of curvature of said right balllens, said right ball lens having a right ball lens pupil; (c) a curvedmirror, said curved mirror having a center of curvature placed opticallymidway between said left ball lens and said right ball lens; (d) abeamsplitter disposed to reflect said left and right curved imagestoward said curved mirror, said curved mirror disposed to form a virtualstereoscopic image of said left and right curved images, and said curvedmirror disposed to form, through said beamsplitter, a real image of saidleft ball lens pupil at said left viewing pupil and a real image of saidright ball lens pupil at said right viewing pupil.
 2. The opticalapparatus of claim 1 wherein said left image generator comprises aliquid crystal device.
 3. The optical apparatus of claim 1 wherein saidleft image generator comprises a digital micromirror device.
 4. Theoptical apparatus of claim 1 wherein said left image generator comprisesa laser.
 5. The optical apparatus of claim 1 wherein said left imagegenerator comprises a cathode-ray tube.
 6. The optical apparatus ofclaim 1 wherein said left image generator comprises a grating lightvalve.
 7. The optical apparatus of claim 1 wherein said right imagegenerator comprises a liquid crystal device.
 8. The optical apparatus ofclaim 1 wherein said right image generator comprises a digitalmicromirror device.
 9. The optical apparatus of claim 1 wherein saidright image generator comprises a laser.
 10. The optical apparatus ofclaim 1 wherein said right image generator comprises a cathode-ray tube.11. The optical apparatus of claim 1 wherein said right image generatorcomprises a grating light valve.
 12. The optical apparatus of claim 1wherein said left spherically curved diffusive surface comprises acoating.
 13. The optical apparatus of claim 1 wherein a fiber opticfaceplate comprises said left spherically curved diffusive surface. 14.The optical apparatus of claim 1 wherein said right spherically curveddiffusive surface comprises a coating.
 15. The optical apparatus ofclaim 1 wherein a fiber optic faceplate comprises said right sphericallycurved diffusive surface.
 16. The optical apparatus of claim 1 whereinsaid curved mirror comprises a plurality of mirror segments.
 17. Theoptical apparatus of claim 16 wherein said plurality of mirror segmentscomprises at least one spherical mirror.
 18. The optical apparatus ofclaim 16 wherein said plurality of mirror segments comprises at leasttwo replicated mirrors.
 19. The optical apparatus of claim 1 whereinsaid curved mirror is essentially spherical.
 20. The optical apparatusof claim 1 wherein said curved mirror comprises a stretched membrane.21. The optical apparatus of claim 1 wherein said curved mirrorcomprises a Fresnel mirror.
 22. The optical apparatus of claim 1 whereinrespective optical axes for said left optical system and for said rightoptical system are disposed at a convergent angle.
 23. The opticalapparatus of claim 1 wherein said left ball lens comprises a centralspherical lens.
 24. The optical apparatus of claim 23 wherein said leftball lens further comprises at least one meniscus lens, wherein bothsurfaces of said meniscus lens share a common center of curvature withsaid central spherical lens.
 25. The optical apparatus of claim 23wherein said central spherical lens comprises a refractive liquid. 26.The optical apparatus of claim 1 wherein said right ball lens comprisesa central spherical lens.
 27. The optical apparatus of claim 26 whereinsaid right ball lens further comprises at least one meniscus lens,wherein both surfaces of said meniscus lens share a common center ofcurvature with said central spherical lens.
 28. The optical apparatus ofclaim 26 wherein said central spherical lens comprises a refractiveliquid.
 29. The optical apparatus of claim 1 wherein said left ball lensis located between 55 mm to 75 mm from said right ball lens.
 30. Theoptical apparatus of claim 1 wherein said curved mirror is cylindrical.31. The optical apparatus of claim 1 wherein said curved mirror istoroidal.
 32. A monocentric autostereoscopic optical apparatus forviewing a stereoscopic virtual image comprising a left image to beviewed by an observer at a left viewing pupil and a right image to beviewed by the observer at a right viewing pupil, the apparatuscomprising: (a) a left optical system for forming said left image to beviewed at said left viewing pupil, the system comprising a leftprojection system comprising a left spherically curved image-formingsurface for forming a left intermediate image, said left sphericallycurved image-forming surface having its center of curvaturesubstantially concentric with a left ball lens, said left ball lensspaced apart from said left spherically curved image-forming surfacesuch that a left curved image is formed, said left curved image being areal image, the center of curvature of said left curved image coincidentwith the center of curvature of said left ball lens, said left ball lenshaving a left ball lens pupil; (b) a right optical system for formingsaid right image to be viewed at said right viewing pupil, the systemcomprising a right projection system comprising a right sphericallycurved image-forming surface for forming a right intermediate image,said right spherically curved image-forming surface having its center ofcurvature substantially concentric with a right ball lens, said rightball lens spaced apart from said right spherically curved image-formingsurface such that a right curved image is formed, said right curvedimage being a real image, the center of curvature of said right curvedimage coincident with the center of curvature of said right ball lens,said right ball lens having a right ball lens pupil; (c) a curvedmirror, said curved mirror having its center of curvature placedsubstantially optically midway between said left ball lens and saidright ball lens; (d) a beamsplitter disposed to reflect said left andright curved images toward said curved mirror, said curved mirrordisposed to form a virtual stereoscopic image of said left and rightcurved images, and said curved mirror disposed to form, through saidbeamsplitter, a real image of said left ball lens pupil at said leftviewing pupil and a real image of said right ball lens pupil at saidright viewing pupil.
 33. The apparatus of claim 32 wherein said leftspherically curved image-forming surface comprises an organic lightemitting diode array.
 34. The apparatus of claim 32 wherein said leftspherically curved image-forming surface comprises a polymer lightemitting diode array.
 35. The apparatus of claim 32 wherein said rightspherically curved image-forming surface comprises an organic lightemitting diode array.
 36. The apparatus of claim 32 wherein said rightspherically curved image-forming surface comprises a polymer lightemitting diode array.
 37. The optical apparatus of claim 32 wherein saidcurved mirror comprises a plurality of mirror segments.
 38. The opticalapparatus of claim 37 wherein said plurality of mirror segmentscomprises at least one spherical mirror.
 39. The optical apparatus ofclaim 37 wherein said plurality of mirror segments comprises at leasttwo replicated mirrors.
 40. The optical apparatus of claim 32 whereinsaid curved mirror is essentially spherical.
 41. The optical apparatusof claim 32 wherein said curved mirror comprises a stretched membrane.42. The optical apparatus of claim 32 wherein said curved mirrorcomprises a Fresnel mirror.
 43. The optical apparatus of claim 32wherein respective optical axes for said left optical system and forsaid right optical system are disposed at a convergent angle.
 44. Theoptical apparatus of claim 32 wherein said left spherically curvedimage-forming surface comprises a cathode-ray tube.
 45. The opticalapparatus of claim 32 wherein said right spherically curvedimage-forming surface comprises a cathode-ray tube.
 46. The opticalapparatus of claim 32 wherein said left ball lens is located between 55mm to 75 mm from said right ball lens.
 47. A monocentricautostereoscopic optical apparatus for viewing a stereoscopic virtualimage comprising a left image to be viewed by an observer at a leftviewing pupil and a right image to be viewed by the observer at a rightviewing pupil, the apparatus comprising: (a) a left optical system forforming said left image to be viewed at said left viewing pupil, thesystem comprising: (1) a left image generation system for providingscene content, comprising a left image generator and a left relay lensfor forming a left intermediate image; (2) a left projection systemcomprising a left spherically curved diffusive surface for acceptingsaid left intermediate image, said left spherically curved surfacehaving its center of curvature substantially concentric with a left balllens, said left ball lens spaced apart from said left spherically curveddiffusive surface such that a left curved image is formed, said leftcurved image being a real image, the center of curvature of said leftcurved image coincident with the center of curvature of said left balllens, said left ball lens having a left ball lens pupil; (b) a rightoptical system for forming said right image to be viewed at said rightviewing pupil, the system comprising: (1) a right image generationsystem for providing scene content, comprising a right image generatorand a right relay lens for forming a right intermediate image; (2) aright projection system comprising a right spherically curved diffusivesurface for accepting said right intermediate image, said rightspherically curved surface having its center of curvature substantiallyconcentric with a right ball lens, said right ball lens spaced apartfrom said right spherically curved diffusive surface such that a rightcurved image is formed, said right curved image being a real image, thecenter of curvature of said right curved image coincident with thecenter of curvature of said right ball lens, said right ball lens havinga right ball lens pupil; (c) a curved mirror, said curved mirror locatedan equal distance from said left and right ball lens and said left andright viewing pupils, said curved mirror disposed to form a virtualstereoscopic image from said left and right curved images, and saidcurved mirror disposed to form a real image of said left ball lens pupilat said left viewing pupil and a real image of said right ball lenspupil at said right viewing pupil.
 48. The optical apparatus of claim 47wherein said left image generator comprises a liquid crystal device. 49.The optical apparatus of claim 47 wherein said left image generatorcomprises a digital micromirror device.
 50. The optical apparatus ofclaim 47 wherein said left image generator comprises a laser.
 51. Theoptical apparatus of claim 47 wherein said left image generatorcomprises a cathode-ray tube.
 52. The optical apparatus of claim 47wherein said left image generator comprises a grating light valve. 53.The optical apparatus of claim 47 wherein said right image generatorcomprises a liquid crystal device.
 54. The optical apparatus of claim 47wherein said right image generator comprises a digital micromirrordevice.
 55. The optical apparatus of claim 47 wherein said right imagegenerator comprises a laser.
 56. The optical apparatus of claim 47wherein said right image generator comprises a cathode-ray tube.
 57. Theoptical apparatus of claim 47 wherein said right image generatorcomprises a grating light valve.
 58. The optical apparatus of claim 47wherein said left spherically curved diffusive surface comprises acoating.
 59. The optical apparatus of claim 47 wherein a fiber opticfaceplate comprises said left spherically curved diffusive surface. 60.The optical apparatus of claim 47 wherein said right spherically curveddiffusive surface comprises a coating.
 61. The optical apparatus ofclaim 47 wherein a fiber optic faceplate comprises said rightspherically curved diffusive surface.
 62. The optical apparatus of claim47 wherein said curved mirror comprises a plurality of mirror segments.63. The optical apparatus of claim 62 wherein said plurality of mirrorsegments comprises at least one spherical mirror.
 64. The opticalapparatus of claim 62 wherein said plurality of mirror segmentscomprises at least two replicated mirrors.
 65. The optical apparatus ofclaim 47 wherein said curved mirror is essentially spherical.
 66. Theoptical apparatus of claim 47 wherein said curved mirror comprises astretched membrane.
 67. The optical apparatus of claim 47 wherein saidcurved mirror comprises a Fresnel mirror.
 68. The optical apparatus ofclaim 47 wherein respective optical axes for said left optical systemand for said right optical system are disposed at a convergent angle.69. The optical apparatus of claim 47 wherein said left ball lenscomprises a central spherical lens.
 70. The optical apparatus of claim69 wherein said left ball lens further comprises at least one meniscuslens, wherein both surfaces of said meniscus lens share a common centerof curvature with said central spherical lens.
 71. The optical apparatusof claim 69 wherein said central spherical lens comprises a refractiveliquid.
 72. The optical apparatus of claim 47 wherein said right balllens comprises a central spherical lens.
 73. The optical apparatus ofclaim 72 wherein said right ball lens further comprises at least onemeniscus lens, wherein both surfaces of said meniscus lens share acommon center of curvature with said central spherical lens.
 74. Theoptical apparatus of claim 47 wherein said left ball lens is locatedbetween 55 mm to 75 mm from said right ball lens.
 75. The opticalapparatus of claim 72 wherein said central spherical lens comprises arefractive liquid.
 76. The optical apparatus of claim 47 wherein saidcurved mirror is cylindrical.
 77. The optical apparatus of claim 47wherein said curved mirror is toroidal.
 78. The optical apparatus ofclaim 47 wherein said curved mirror is elliptical.
 79. A monocentricautostereoscopic optical apparatus for viewing a stereoscopic virtualimage comprising a left image to be viewed by an observer at a leftviewing pupil and a right image to be viewed by the observer at a rightviewing pupil, the apparatus comprising: (a) a left optical system forforming said left image to be viewed at said left viewing pupil, thesystem comprising a left projection system comprising a left sphericallycurved image-forming surface for forming a left intermediate image, saidleft spherically curved image-forming surface having its center ofcurvature substantially concentric with a left ball lens, said left balllens spaced apart from said left spherically curved image-formingsurface such that a left curved image is formed, said left curved imagebeing a real image, the center of curvature of said left curved imagecoincident with the center of curvature of said left ball lens, saidleft ball lens having a left ball lens pupil; (b) a right optical systemfor forming said right image to be viewed at said right viewing pupil,the system comprising a right projection system comprising a rightspherically curved image-forming surface for forming a rightintermediate image, said right spherically curved image-forming surfacehaving its center of curvature substantially concentric with a rightball lens, said right ball lens spaced apart from said right sphericallycurved image-forming surface such that a right curved image is formed,said right curved image being a real image, the center of curvature ofsaid right curved image coincident with the center of curvature of saidright ball lens, said right ball lens having a right ball lens pupil;(c) a curved mirror, said curved mirror located an equal distance fromsaid left and right ball lens and said left and right viewing pupils,said curved mirror disposed to form a virtual stereoscopic image fromsaid left and right curved images and said curved mirror disposed toform a real image of said left ball lens pupil at said left viewingpupil and a real image of said right ball lens pupil at said rightviewing pupil.
 80. The apparatus of claim 79 wherein said leftspherically curved image-forming surface comprises an organic lightemitting diode array.
 81. The apparatus of claim 79 wherein said leftspherically curved image-forming surface comprises a polymer lightemitting diode array.
 82. The apparatus of claim 79 wherein said rightspherically curved image-forming surface comprises an organic lightemitting diode array.
 83. The apparatus of claim 79 wherein said rightspherically curved image-forming surface comprises a polymer lightemitting diode array.
 84. The optical apparatus of claim 79 wherein saidcurved mirror comprises a plurality of mirror segments.
 85. The opticalapparatus of claim 84 wherein said plurality of mirror segmentscomprises at least one spherical mirror.
 86. The optical apparatus ofclaim 79 wherein said curved mirror is toroidal.
 87. The opticalapparatus of claim 79 wherein said curved mirror is elliptical.
 88. Theoptical apparatus of claim 84 wherein said plurality of mirror segmentscomprises at least two replicated mirrors.
 89. The optical apparatus ofclaim 79 wherein said curved mirror is essentially spherical.
 90. Theoptical apparatus of claim 79 wherein said curved mirror comprises astretched membrane.
 91. The optical apparatus of claim 79 wherein saidcurved mirror comprises a Fresnel mirror.
 92. The optical apparatus ofclaim 79 wherein respective optical axes for said left optical systemand for said right optical system are disposed at a convergent angle.93. The optical apparatus of claim 79 wherein said left sphericallycurved image-forming surface comprises a cathode-ray tube.
 94. Theoptical apparatus of claim 79 wherein said right spherically curvedimage-forming surface comprises a cathode-ray tube.
 95. The opticalapparatus of claim 79 wherein said left ball lens is located between 55mm to 75 mm from said right ball lens.
 96. A method for display of astereoscopic virtual image to an observer, the image comprising a leftimage to be viewed by the observer at a left viewing pupil and a rightimage to be viewed by the observer at a right viewing pupil, the methodcomprising the steps of: (a) forming a left intermediate image on a leftspherically curved diffusive surface, said left spherically curveddiffusive surface having a center of curvature coincident with a leftball lens, said left ball lens having a left ball lens pupil; (b)projecting said left intermediate image by said left ball lens to form aleft curved image near the front focal surface of a curved mirror; (c)forming a left virtual image from said left curved image, said leftvirtual image viewable from said left viewing pupil, said left viewingpupil formed by said curved mirror as an image of said left ball lenspupil; (d) forming a right intermediate image on a right sphericallycurved diffusive surface, said right spherically curved diffusivesurface having a center of curvature coincident with a right ball lens,said right ball lens having a right ball lens pupil; (e) projecting saidright intermediate image by said right ball lens to form a right curvedimage near the front focal surface of said curved mirror; (f) forming aright virtual image from said right curved image, said right virtualimage viewable from said right viewing pupil, said right pupil formed bysaid curved mirror as an image of said right ball lens pupil.
 97. Themethod of claim 96 wherein the step of forming said left intermediateimage on a left spherically curved diffusive surface further comprisesthe steps of: (a) modulating a light source using a spatial lightmodulator to form a source image comprising an array of pixels; (b)relaying said source image from said spatial light modulator onto saidleft spherically curved diffusive surface.
 98. The method of claim 96wherein the step of forming said right intermediate image on a rightspherically curved diffusive surface further comprises the steps of: (a)modulating a light source using a spatial light modulator to form asource image comprising an array of pixels; (b) relaying said sourceimage from said spatial light modulator onto said right sphericallycurved diffusive surface.
 99. The method of claim 96 wherein the step offorming said left intermediate image on said left spherically curveddiffusive surface comprises the step of forming an image on an organicLED array surface.
 100. The method of claim 96 wherein the step offorming said left intermediate image on said left spherically curveddiffusive surface comprises the step of forming an image on a polymerLED array surface.
 101. The method of claim 96 wherein the step ofprojecting said left intermediate image to form said left curved imagefurther comprises the intermediate step of projecting said leftintermediate image through a beamsplitter.
 102. The method of claim 96wherein the step of forming said right intermediate image on said rightspherically curved diffusive surface comprises the step of forming animage on an organic LED array surface.
 103. The method of claim 96wherein the step of forming said right intermediate image on said rightspherically curved diffusive surface comprises the step of forming animage on a polymer LED array surface.
 104. The method of claim 96wherein the step of projecting said right intermediate image to formsaid right curved image further comprises the intermediate step ofprojecting said right intermediate image through a beamsplitter. 105.The optical apparatus of claim 96 wherein said left ball lens is locatedbetween 55 mm to 70 mm from said right ball lens.